1. Field of the Invention
The present invention relates to image analysis.
2. Description of the Related Art
An image analysis technique called fluorescence cross-correlation spectroscopy (FCCS) has been known. FCCS is disclosed in, for example, Michelle A. Digman, Claire M. Brown, Parijat Sengupta, Paul W. Wiseman, Alan R. Horwitz, and Enrico Gratton, “Measuring Fast Dynamics in Solutions and Cells with a Laser Scanning Microscope”, Biophysical Journal, Vol. 89, pp. 1317-1327, August 2005. FCCS is designed to perform correlation analysis by continuously irradiating one or more measurement points in a sample with excitation light for a certain period of time (e.g., 10 sec) and detecting fluctuations in the intensity of fluorescence emitted from the measurement points, thereby estimating the number of molecules and a diffusion constant.
In addition, an image analysis technique called raster image correlation spectroscopy (RICS) is also known. RICS is disclosed in, for example, non-patent literature 2. RICS is designed to acquire a raster scanned image(s) of one or more frames. A raster scanned image can be, for example, a fluorescence image. The data of each pixel of a fluorescence image represents the information of the intensity of fluorescence emitted from a corresponding point in a sample. The data of pixels differ in acquisition time and position.
Correlation characteristics based on molecular fluctuations are obtained by performing spatial autocorrelation analysis using the data of these pixels. A diffusion constant and the number of molecules can be obtained from the correlation characteristics of molecules. A molecular diffusion time can be obtained from the diffusion constant. A molecular weight can be obtained from the molecular diffusion time.
Since a molecular weight, the number of molecules, and the like can be evaluated by performing spatial autocorrelation analysis in this manner, it is possible to observe interactions between molecules.
In FCCS, since measurement points in a sample are irradiated with excitation light for a relatively long period of time, the sample tends to be damaged. In addition, a target that can be analyzed is limited to a sample with a short diffusion time, and this analysis technique cannot be applied to a sample with a relatively long diffusion time.
In contrast to this, in RICS, since each point in a sample is irradiated with excitation light for a relatively short period of time, the damage of the sample is small. In addition, RICS can be effectively applied to a sample with a relatively long diffusion time.
Conventionally, an analysis based on RICS has been done to calculate the diffusion time of molecules (or the number of molecules) by using the image data of one region. The analysis result is the evaluation of the motions of molecules in the region. Such an analysis cannot evaluate the motions of molecules between different regions.